Apparatus for storing and moving a cassette

ABSTRACT

A cassette stocker includes a plurality of cassette storage shelves positioned adjacent a cleanroom wall and vertically disposed relative to a plurality of cassette docking stations, and a cassette mover to carry a cassette between the shelves and the docking stations. An interstation transfer apparatus includes a support beam and a transfer arm adapted to carry a cassette between processing stations.

This application is a continuation of U.S. patent application Ser. No.10/263,163, filed Oct. 2, 2002, which is a division of U.S. patentapplication Ser. No. 09/527,092, filed Mar. 16, 2000 and issued as U.S.Pat. No. 6,506,009 on Jan. 14, 2003. Each of the above patentapplications is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to substrate processing, andmore particularly to an apparatus for storing and moving substratecassettes.

BACKGROUND OF THE INVENTION

Semiconductor devices are made on substrates, such as silicon wafers orglass plates, for use in computers, monitors, and the like. Thesedevices are made by a sequence of fabrication steps, such as thin filmdeposition, oxidation or nitration, etching, polishing, and thermal andlithographic processing. Although multiple fabrication steps may beperformed in a single processing station, substrates must be transportedbetween different processing stations for at least some of thefabrication steps. In addition, random substrates in a particular batchmay be tested using metrology devices which require additional stations.Substrates are stored in cassettes for transfer between processingstations, metrology stations and other locations. Although cassettes maybe carried manually between processing stations, the transfer ofcassettes is typically automated. For example, a cassette may betransported to a processing station in an automatic guided vehicle(AGV), and then loaded from the AGV onto a loading platform in theprocessing station by a robot. Another robot may extract a substratefrom the cassette and transport it into a processing chamber at theprocessing station. When the fabrication steps are complete, thesubstrate is loaded back into the cassette. Once all of the substrateshave been processed and returned to the cassette, the cassette isremoved from the loading platform and transported to another location bythe AGV.

In order to ensure that the processing equipment does not sit idle, anearly continuous supply of unprocessed substrates should be availableat the processing station. Unfortunately, many processing stations canhold only a single cassette at the loading platform. Therefore, once allof the substrates in the cassette have been processed, the cassette mustbe quickly replaced, either manually or by an AGV, with a new cassettecontaining unprocessed substrates. Running such a just-in-time cassetteinventory system requires either significant operator oversight or alarge number of AGVs, thereby increasing the costs of the fabricationfacility.

Therefore, there is a need for a method and apparatus which continuouslysupplies substrate cassettes to a processing system so that system downtime is reduced or eliminated.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for storingmultiple cassettes at a processing station, ensuring that a nearlycontinuous supply of unprocessed substrates is available for processingand that the processing equipment does not idle. Multiple cassettes canbe stored at a processing station in a front end support frame and acassette can be moved to one of a plurality of vertically disposeddocking stations where substrates are extracted and transferred to theprocessing equipment. An automation system is mounted or otherwisedisposed on the frame to transfer cassettes between docking stations orbetween processing stations. In another aspect of the invention,cassettes can be transported between different processing stationswithout the use of an AGV.

In one aspect of the invention, an apparatus is provided which includesa front end frame having a plurality of vertically disposed dockingstations and multiple cassette storage stations. An automated transferassembly is preferably disposed adjacent the docking stations and thestorage stations to move cassettes between the storage stations and thedocking stations. Additionally, an automated transfer assembly can belocated between processing stations to transfer cassettes betweenprocessing stations without the need for manual or AGV assistance. Inanother aspect of the invention, a method is provided for delivering acontinuous supply of cassettes to a processing system. The methodpreferably includes providing a plurality of vertically disposed dockingstations and multiple storage stations and moving cassettes between thestorage stations and the transfer stations to ensure that substrates arecontinually supplied to the processing system. Additionally, a method isprovided for transferring cassettes between processing stations tocontinue the processing sequence without the need for manual or AGVassistance.

Other objects, features and advantages of the present invention willbecome more fully apparent from the following detailed description ofthe preferred embodiments, the appended claims and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top view of a processing station according to thepresent invention;

FIG. 2 is a schematic perspective view of a cassette for holdingsubstrates;

FIG. 3 is a schematic perspective view of a cassette stocker accordingto the present invention;

FIG. 4A is a schematic front view of the cassette stocker of FIG. 3;

FIG. 4B is a schematic front view of the cassette stocker of FIG. 4Awith a plurality of cassettes;

FIG. 5A is a schematic side view of the cassette stocker of FIG. 3;

FIG. 5B is a schematic side view of the cassette stocker of FIG. 3 witha plurality of cassettes;

FIG. 6 is a schematic top view of an end effector located over a dockingstation;

FIGS. 7A, 7B and 7C are schematic perspective views illustrating the endeffector of FIG. 6 lifting and moving a cassette;

FIGS. 8A and 8B are schematic front views of the cassette stocker ofFIG. 3 illustrating the path the end effector of FIG. 6 takes in movinga cassette between a loading platform and a cassette docking platform;

FIG. 9 is a schematic perspective view of another embodiment of acassette stocker having a plurality of vertically disposed dockingstations;

FIG. 10 is a schematic side view of the cassette stocker of FIG. 9;

FIG. 11 is a schematic side view of the cassette stocker of FIG. 9 witha plurality of cassettes;

FIG. 12 is a schematic front view of two loading and storage stationsconnected by an interstation transfer mechanism;

FIG. 13 is a schematic front view of a cassette stocker having a singlepair of vertically disposed docking stations; and

FIG. 14 is a simplified side schematic view of a cassette stocker havinga single pair of vertically disposed docking stations, the doors ofwhich open in opposite directions.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In the following description, the term “substrate” broadly covers anyobject that is being processed in a semiconductor device processingsystem. The term “substrate” includes, for example, semiconductorwafers, flat panel displays, glass plates or disks, and plasticworkpieces.

FIG. 1 is a top view of a processing station 20 of the present inventionin which one or more substrates 10 are processed. The processing station20 has a front-end staging area 22 which is separated from a loading andstorage area 24 by a cleanroom wall 26. Cleanroom wall 26 separates acleanroom 28, where loading and storage area 24 is located, from a grayarea 30, where a processing system 32 is housed. The loading and storagearea 24 is where cassettes of substrates are delivered andloaded/unloaded into/from the processing station 20. Processing system32 may include one or more load lock chambers 34, a central transferchamber 36, and a plurality of processing chambers 38. Inside processingchambers 38 the substrate may be subjected to a variety of fabricationsteps, such as thin film deposition, oxidation, nitration, etching,thermal processing or lithographic processing. The processing system andstaging area illustrated in FIG. 1 are merely representative. Theprocessing system could have just a single processing chamber, or itcould be a device, such as a chemical mechanical polisher, that does notinclude any processing chambers. In addition, the processing systemcould include metrology devices instead of or in addition to processingdevices.

Referring to FIGS. 1 and 2, one or more substrates 10 are brought to theloading and storage area 24 of the processing station in a cassette 100.Substrates 10 are supported in cassette 100 in a generally parallelhorizontal configuration by slot ridges 102. Substrates may be loadedand unloaded from cassette 100 through an entry port 103 located in agenerally flat front face 106 of the cassette. A removable cassette door104 may be secured to entry port 103 to prevent the substrates frombeing exposed to contaminants when the cassette is moved betweenprocessing stations or stored outside a processing station. Eachcassette 100 also includes three cylindrical indentations 108 (shown inphantom and only two of which are visible in FIG. 2) formed in anunderside 110 of the cassette. When cassette 100 is stored at theprocessing station, three support pins will fit into indentations 108 tosupport the cassette. Two handles 112 (only one is shown in thisperspective view) which project from sidewalls 114 may be used tomanually carry the cassette. A generally rectangular flange 116 havingan L-shaped cross-section projects from a top surface 118 of thecassette. As discussed below, a robotic cassette mover at the processingstation may manipulate the cassette by means of flange 116.

Referring to FIGS. 1-5B, loading and storage area 24 of processingstation 20 includes a cassette loading platform 52, two cassettesubstrate transfer or docking stations 40 located on either side ofloading platform 52, and a cassette stocker or storage stations 50 (onlypartially illustrated in FIG. 1 so that docking stations 40 may be seen)for storing cassettes at the processing station and moving the cassettesto and from loading platform 52 and docking stations 40.

A cassette 100 may be placed on or removed from loading platform 52either manually or by an AGV. From the loading platform 52, the cassette100 may be moved to one of docking stations 40 or into cassette stocker50. Loading platform 52 has generally the same perimeter shape as acassette. Three support pins 64 (only two are shown in the side view ofFIG. 5A) project vertically from the loading platform 52 to mate withthe indentations in the underside of the cassette 100 and thus to securethe cassette on the loading platform 52.

To transfer substrates through the cleanroom wall 26, cassettes 100(shown in phantom in FIG. 1) may be positioned at one or both dockingstations 40. Each docking station 40 includes a docking platform 42 tosupport a cassette, an opening 46 formed through cleanroom wall 26, amovable door 44 which seals opening 46 when a substrate is not to betransferred through opening 46 or when a cassette is not positioned ondocking platform 42, and a mechanism to unlock cassette door 104 andretract the door 104 into front-end staging area 22 to providehorizontal access to the substrates stored within the cassette. Forexample, the moveable door 44 may behave as a “receiver” and receive thecassette door 104 of a cassette, and then move below the opening 46(carrying the cassette door 104) so as to allow horizontal accessthrough the opening 46 to substrates stored within the cassette. Adescription of the preferred configuration and operation of dockingstation 40 may be found in U.S. patent application Ser. No. 09/012,323,entitled “A Wafer Cassette Load Station”, filed Jan. 23, 1998, by EricA. Nering, et al., assigned to the assignee of the present invention,the entire disclosure of which is incorporated herein by reference.

Cassette stocker 50 includes a frame 60 that supports one or morestorage racks 58 (shown in FIG. 4A and not illustrated in FIG. 1 so thatthe docking stations may be shown), and a robotic cassette mover 56 tomove the cassettes between the storage rack 58, the loading platform 52,and the docking platforms 42. Frame 60 may be bolted to the floor ofcleanroom 28 and/or secured to the cleanroom wall 26. The frame 60 is atleast partially disposed below the docking platforms 42 and loadingplatform 52 so that the footprint of processing station 20 is minimallyincreased if increased at all.

Storage rack 58 may include a vertical column of support shelves 62above each of the two docking stations 40. Each column may include, forexample, one, two, three or more individual support shelves 62. Thus,storage rack 58 shown in FIGS. 3-5B provides storage space for sixcassettes 100 in support shelves 62 a -62 f (see FIG. 4B). Each supportshelf, such as support shelf 62 a, may be a horizontally oriented platehaving substantially the same perimeter shape as the cassette 100. Threesupport pins 64 (only two are shown in the side view of FIG. 5A) projectvertically from the support shelf 62 and are positioned to mate withreceiving indentations 108 in the underside of the cassette 100. Twovertical posts 66 may be used to secure the outer edge of each supportshelf 62 a -62 f to frame 60. Additionally, the support shelves 62 couldbe secured to the cleanroom wall for additional support.

Robotic cassette mover 56 is used to move cassettes 100 between thestorage shelves 62, the loading platform 52 and the docking platforms42. The robotic cassette mover 56 includes a vertically movable endeffector 72 which is attached to a horizontally movable support strut74. The support strut 74 permits arbitrary horizontal movement of endeffector 72 in a plane parallel to cleanroom wall 26. The bottom ofsupport strut 74 may be secured to a lateral slider 76 which can movehorizontally along a horizontal guide 78 that is attached to or formedas part of frame 60. The lateral slider 76 may be driven fromside-to-side by a horizontal lead screw 80, which is rotated by ahorizontal drive motor 82. The horizontal drive motor 82 may be securedto frame 60. Similarly, end effector 72 may be attached to a verticalslider 84 (FIG. 4B) which can slide vertically along a vertical guide 86(FIG. 5B) attached to or formed as part of support strut 74. Thevertical slider 84 may be driven up and down by a vertical lead screw 87(shown in phantom in FIGS. 4A-5B) which may be rotated by a verticaldrive motor 88. The vertical drive motor may be supported by lateralslider 76. Horizontal drive motor 82 and vertical drive motor 88 may beconnected to a control system (not shown), such as a programmabledigital computer, to control the vertical and horizontal motion of endeffector 72. The actuators which drive the movement of the end effector72 may include stepper motors, pneumatic actuators and other devicesknown to impart movement in a controllable manner. In addition, a beltdrive assembly or other known mechanism can be utilized to drive thesliders both vertically and horizontally.

Referring to FIGS. 6-7A, end effector 72 projects horizontally fromsupport strut 74 toward cleanroom wall 26. The end effector 72 includesa generally flat, hook-shaped finger 90 that defines a rectangular gap92 which is open on one side of the end effector 72. The end effector 72is adapted to engage a portion of a cassette 100 through the use of theopen end of the end effector 72. In order to transport cassette 100, endeffector 72 is vertically positioned between flange 116 and top surface118 of cassette 100. Referring to FIG. 7B, the end effector 72 is movedlaterally so that a base 117 of flange 116 fits into gap 92. Finally,referring to FIG. 7C, end effector 72 is moved vertically upward so thatan inner rim 94 of the end effector 72 contacts an underside 119 offlange 116 to lift the cassette 100. The end effector 72 may then bemoved laterally to carry cassette 100 to another support shelf 62 or tothe loading platform 52 or to a docking platform 42.

Referring to FIGS. 7A-8A, a cassette 100 may be transported from loadingplatform 52 to a support shelf, such as support shelf 62 c. With supportstrut 74 positioned to the side of loading platform 52, a cassette 100is loaded onto the loading platform 52, either manually or by an AGV. Tolift the cassette 100 off loading platform 52, end effector 72 ispositioned to the left of the cassette at a vertical height betweenupper surface 118 of the cassette 100 and the lower surface of flange116. The support strut 74 moves rightwardly until end effector 72engages the support flange (phantom line A). Then, the end effector 72moves upwardly to raise the cassette 100 off of the loading platform 52(phantom line B). To move the cassette 100 to one of the supportshelves, e.g., support shelf 62 c, end effector 72 raises the cassette100 until the cassette 100 is generally aligned above the support shelf62 c, with sufficient vertical clearance to permit the underside of thecassette 100 to move horizontally over support pins 64 (phantom line C).Then support strut 74 is moved leftwardly to position the cassette 100over the support shelf 62 c, and the end effector 72 moves downwardlyuntil the cassette 100 rests on support pins 64 (phantom line D). Theend effector 72 may be withdrawn by moving it leftwardly until it clearsthe flange 116, and then moving it upwardly and rightwardly between thetop of the flange 116 and the bottom of support shelf 62 b (phantom lineE).

Referring to FIG. 8B, in order to remove the cassette 100 from supportshelf 62 c, these steps are generally repeated in reverse order.Specifically, end effector 72 moves leftwardly between the top of flange116 and the bottom of support shelf 62 b (phantom line F), downwardlyuntil the end effector 72 is located at a vertical position between thetop surface of the cassette 100 and the underside of the flange 116(phantom line G), and rightwardly until it engages the flange 116(phantom line H). Then the end effector 72 moves upwardly to lift thecassette 100 off the support plate 62 b and then rightwardly to carrythe cassette 100 into the vertical channel between the storage racks 58(phantom line I). From this position, the cassette 100 may be moved upor down and then left or right to a new storage shelf, to one of thedocking platforms 42, or to the loading platform 52.

In the embodiments described in FIGS. 7A-8B, hook-shaped finger 90 ofend effector 72 curves to the right so that rectangular gap 92 is openon the right. Of course, if hook-shaped finger 90 curved to the left sothat rectangular gap 92 was open on the left, then the relative lateralmotion of the end effector to engage and disengage the cassette 100would be reversed. For example, to lift the cassette 100 from a supportshelf 62 b, the end effector 72 would be positioned on the right side ofthe cassette 100 and moved leftwardly to engage the flange 116.

Referring to FIGS. 1-3, in operation a cassette 100 is transported toprocessing station 20 and placed on loading platform 52, e.g., manuallyor by an AGV. The robotic cassette mover 56 transports the cassette fromthe loading platform 52 to one of the docking stations 40, which alignsthe front face of the cassette 100 with docking station door 44. Dockingstation door 44 then retracts, opening cassette door 104 so that entryport 102 mates with opening 46 in cleanroom wall 26. A wafer handlingrobot 48 in front-end staging area 22 extracts the substrates from thecassette 100 through opening 46 in the cleanroom wall 26 and inserts thesubstrates into one of the load lock chambers 34. A robot 39 in transferchamber 36 moves substrates between the load lock 34 and the processingchambers 38. When the fabrication steps are complete, wafer handlingrobot 48 extracts the substrate from one of the lock load chambers 34,and returns the substrate to cassette 100 through opening 46 incleanroom wall 26. Once all of the substrates have been processed,cassette door 104 is closed, the cassette 100 is moved to storage rack58 or loading platform 52, and a new cassette 100 containing unprocessedsubstrates is loaded onto the docking station 40.

As stated above, the processing system could perform inspectionprocesses using metrology devices instead of or in addition tofabrication steps. Metrology stations typically sample and testprocessed and/or unprocessed wafers stored within the wafer cassettes100. Typically, a metrology station may test as few as one wafer withineach wafer cassette 100 selected for metrology, the cassette 100 beingselected randomly or based on some pre-determined selection criteriaaccording to standard metrology principles. Accordingly, each wafercassette 100 presented for metrology may have significantly lessresident time at a particular docking station 40 operated in connectionwith a metrology station than if the wafer cassette 100 were presentedfor processing in a processing station. As a result, the time requiredto open and close the doors and the time required to move a firstcassette 100 from the docking station 40 and replace the first cassette100 with a second cassette 100 may result in undesirable downtime of themetrology station if only one or two docking stations 40 are employed.Further, certain processing stations, particularly those with shortprocessing times, may also have unnecessary downtime as a result ofusing only one or two docking stations 40.

Therefore, it may be desirable to incorporate a plurality of verticallystacked docking stations in connection with each storage rack 58. FIGS.9-11 illustrate a stacked docking station embodiment of a loading andstorage area 24 of processing station 20 having two lower substratedocking stations 40 and two upper substrate docking stations 540. As inthe previous embodiments, the loading and storage area 24 of processingstation 20 includes a cassette loading platform 52, two lower cassettedocking or substrate transfer stations 40 located on either side ofloading platform 52, and cassette stocker or storage stations 50 forstoring cassettes 100 at the processing station and moving the cassettes100 to and from loading platform 52 and docking stations 40. Thisembodiment, however, also includes two upper cassette docking orsubstrate transfer stations 540 each of which is located above one ofthe docking stations 40. The docking stations thus at least partiallyoverlap, and preferably completely overlap, in footprint. The verticallydisposed docking stations are also vertically disposed relative to oneor (preferably) more of the support shelves 62.

According to this embodiment, a cassette 100 may be placed onto orremoved from loading platform 52 either manually or by an AGV. Totransfer substrates through the cleanroom wall 26, cassettes 100 may bepositioned at one of the lower docking stations 40 or also at one of theupper docking stations 540. Each lower docking station 40 includes alower docking platform 42 to support a cassette 100, a lower opening 46formed through cleanroom wall 26, a lower movable door 44 which sealslower opening 46 when a substrate is not to be transferred through loweropening 46 or when a cassette 100 is not positioned on lower dockingplatform 42, and a mechanism to unlock cassette door 104 and retract thedoor 104 into front-end staging area 22 so as to provide horizontalaccess to the substrate. Each upper docking station 540 likewiseincludes an upper docking platform 542 to support a cassette, an opening546 formed through cleanroom wall 26, an upper movable door 544 whichseals upper opening 546 when a substrate is not to be transferredthrough upper opening 546 or when a cassette 100 is not positioned onupper docking platform 542, and a mechanism to unlock cassette door 104and retract the door 104 into front-end staging area 22 to providehorizontal access to the substrate.

Upper docking station 540 is of similar construction and operation aslower docking station 40. Similarly, upper movable door 544 is ofsimilar construction and operation as lower movable door 44. Suitablespace is provided between upper opening 546 and lower opening 46 so thatdownward movement of the upper movable door 544 does not interfere withthe operation of lower movable door 44 as will be readily appreciated byone of ordinary skill in the art. In an alternative embodiment, uppermovable door 544 could be arranged to open upwardly allowing the twodoors 44, 544 and the two docking stations 540, 40 to be located closertogether (as shown in FIG. 14). It will also be readily appreciated byone of ordinary skill in the art that transport of the cassette 100 toupper docking platform 542 and operation of the system are similar tothat described in other embodiments. The embodiment described herein hasan upper and lower docking station 40, 540 associated with each of thestorage racks 58. However, it should be noted that a plurality of upperdocking stations 540 may be used limited only by available verticalspace. Further, the upper docking station 540 and the lower dockingstation 40 may be separated by one or more of the support shelves 62, orboth the upper and lower docking stations may be positioned above one ormore of the plurality of storage shelves 62.

The embodiment described above also includes two storage racks 58disposed above two pairs of docking stations 40, 540 and a loadingstation 52 disposed between the two docking stations. Preferably, sixcassette support shelves 62 a-f are disposed above the docking stations40, 540. While this configuration is believed to provide the highestthroughput of substrates in the available space, the invention alsoincludes a single pair of docking stations 40, 540 as shown in FIG. 13with one or more cassette support shelves 62 disposed in proximity tothe docking stations 40, 540.

FIG. 9 is a perspective view of one embodiment of the invention havingtwo pairs of docking stations 40, 540 and three storage shelves 62 a-cor 62 d-f disposed above each of the pair of docking stations 40, 540.While three support shelves 62 a-c or 62 d-f are shown, only one supportshelf 62 a or 62 d could also be used advantageously. Components whichform a part of the earlier described embodiments are identified usingthe same reference numerals. FIGS. 10 and 11 further depict dockingstations 40, 540 and storage shelves 62 a-c in a side view, shown withand without cassettes, respectively. Referring to FIG. 12, aninterstation transfer apparatus 120 may be used to move cassettes 100between adjacent processing stations 20′ and 20″, thereby eliminatingthe need for AGVs or manual transport. Interstation transfer apparatus120 includes an overhead support beam 122 which may be secured to posts66′ and 66″ of adjacent cassette stockers 50′ and 50″. A transfer arm124 may be attached to a slider 126 that moves horizontally along aguide 127 that is attached to or formed as part of support beam 122. Theslider 126 may be moved horizontally by a lead screw 130 which may berotated by a horizontal drive motor 132. An end effector 128 may beconnected to transfer arm 124 by a pneumatic actuator 134 to provide endeffector 128 with a short vertical stroke.

In order to transport the cassettes 100 between adjacent processingstations 20′, 20″, the cassette 100 is moved by robotic cassette mover56′ to the upper right-hand support shelf, i.e., support shelf 62 d′, ofcassette stocker 50′. End effector 128 moves horizontally over flange116, then down to a vertical position between the bottom of the flangeand the top of the cassette. Then the end effector 128 moves to theright until it engages the cassette flange 116. End effector 128 liftsthe cassette 100 off support plate 62 d′, and horizontal drive motor 132drives the transfer arm 124 rightwardly until the cassette 100 islocated over the upper left-hand support shelf 62 a″ of cassette stocker50″. Finally, the end effector 128 lowers the cassette 100 onto supportshelf 62 a″ and withdraws.

Interstation transfer apparatus 120 provides an extremely simple methodof transferring cassettes 100 between adjacent processing stations 20′,20″. This may be particularly useful where one of the processingstations is a metrology station (which could be located entirely insidethe cleanroom 28), since it permits the metrology measurements to bemade without building a metrology apparatus into the processingequipment 20′, 20″ and without using a factory automation system 22.

Although cassette stockers 50′ and 50″ are illustrated as positionedagainst the same cleanroom wall 26, the interstation transfer apparatus120 could include rotary mechanisms to allow handoff between endeffectors 128 on different support beams. This would permit processingstations 20′ and 20″ to be positioned around the corners or at oppositewalls of the cleanroom.

The embodiments described above include two storage racks 58, eachdisposed above docking stations 40, 540 and a loading station 52disposed between the two storage racks 58. Preferably, six cassettesupport shelves 62 a-f are disposed above each of the one or moredocking stations. While this configuration is believed to provide thehighest throughput of substrates in the available space, the inventionalso includes a single pair of docking stations 40, 540 with one or morecassette support shelves 62 disposed in proximity to the dockingstations 40, 540. FIGS. 13 and 14 are front views of cassette stockershaving a single pair of docking stations 40, 540 and two storage shelves62 a-b disposed above the docking stations 40, 540. The upper moveabledoor 544 opens downwardly in FIG. 13, and upwardly in FIG. 14. When theupper door 544 opens upwardly as shown in FIG. 14, the two dockingstations 540, 40 can be located closer together so as to reduce theoverall height of the cassette stocker. In both embodiments of FIGS. 13and 14 support shelf 62 a is shown in phantom to indicate that only onesupport shelf 62 b could be advantageously used. An enclosure 550 isdisposed about the docking stations 40, 540, the loading station 52 andthe cassette support shelves 62. Components which form a part of theearlier described embodiments are identified using the same numbers.

Substrates may be loaded into the system 20 at either a docking station40, 540 position, at any one of the storage shelf positions 62 or at aloading station 52. The loading station 52 could be disposed adjacenteither a support shelf 62 or a docking station 40, 540. The substratemover system described above with reference to the other embodiments isutilized with the single stack embodiment of FIG. 13 and operates in thesame manner except that support shelves 62 disposed in a single stackeliminate the transfer sequence from the additional stack.

Each of the embodiments described herein utilizes available space aboveor below docking stations, thereby increasing the storage capability ofthe system without increasing the footprint (area occupied by the systemmeasured in terms of floor space) of the system. Although the storageshelves shown herein are located above the pair of docking stations, itwill be understood that one or more storage shelves could be locatedbelow, or between the plurality of vertically disposed docking stations.Accordingly, a processing system could utilize any configuration of thestorage device of the present invention including cassette supportshelves disposed adjacent a docking station. Further, although avertically arranged pair of docking stations is preferably associatedwith each stack of one or more support shelves, a pair of horizontallydisposed docking stations may be associated with each stack of supportshelves. In such a horizontal configuration each docking station iscoupled to a separate tool. The separate tools are preferably highthroughput tools (metrology tools, etc.). Preferably, a cassette moveris also disposed in proximity to the support shelves and the dockingstation to effect transfer of cassettes between the support shelves andthe docking stations. Accordingly, while the present invention has beendisclosed in connection with the preferred embodiments thereof, itshould be understood that other embodiments may fall within the spiritand scope of the invention, as defined by the following claims.

1. A fabrication system, comprising: a first processing station adaptedto perform a process on a substrate, the first processing stationadapted having a first docking station, a first frame, a plurality ofcassette storage shelves fixedly mounted on the first frame andpositioned above the first docking station, a second docking stationpositioned above the first docking station, and a cassette mover mountedon the first frame to carry a cassette among the plurality of shelvesand the first and second docking stations; a second processing stationadapted to perform a process on a substrate, the second processingstation having a third docking station, a second frame, a plurality ofcassette storage shelves fixedly mounted on the second frame andpositioned above the third docking station, a fourth docking stationpositioned above the third docking station and a cassette mover mountedon the second frame to carry a cassette between the plurality of shelvesand the third and fourth docking stations; and an interstation cassettemover adapted to transport a cassette between the first processingstation and the second processing station.
 2. The fabrication system ofclaim 1, wherein the first processing station performs a firstfabrication step.
 3. The fabrication system of claim 1, wherein at leastone of the first and second processing stations is a metrology system.4. The fabrication system of claim 1, wherein the shelves and the firstand second docking stations of the first processing station are arrangedin vertical columns, the shelves and the third and fourth dockingstations of the second processing station are arranged in verticalcolumns, and the interstation cassette mover transports a cassettebetween a topmost shelf of each of the first and second processingstations.
 5. The fabrication system of claim 1, wherein the interstationcassette mover includes a support member positioned adjacent the shelvesand movable in a path parallel to a cleanroom wall, and an end effectorconfigured to engage a cassette, the end effector adapted to movevertically relative to the support member.
 6. The apparatus of claim 1,wherein an upper one of the vertically disposed docking stationscomprises a door adapted to open upwardly, and a lower one of thevertically disposed docking stations comprises a door adapted to opendownwardly.
 7. The fabrication system of claim 1, wherein theinterstation cassette mover includes: a support member positionedadjacent the shelves and movable in a path parallel to a cleanroom wall;an end effector configured to engage a cassette and adapted to movevertically relative to the support member; and a supporting part mountedbetween the respective frames of the first and second processingstations, the support member being movably mounted on the supportingpart.
 8. The fabrication system of claim 5, wherein the interstationcassette mover further includes a supporting part mounted between theplurality of cassette storage shelves of the first processing stationand the plurality of cassette storage shelves of the second processingstation, and wherein the supporting member is movably mounted on thesupporting part.